1. Field of the invention
The present invention relates to a method and apparatus for treating or washing a surface of semiconductor wafer, and more particularly, to a method and an apparatus which eliminates impurities such as particles, microbe, bacillus, silica, etc. clinging on the wafer and an exposure material to be used for an etching treatment.
2. Prior Art
As one of conventional surface treatment apparatuses for semiconductor wafers, a wet surface treatment apparatus called "multi-tank batch type" is disclosed, for example, on page 290-293 of The Handbook of Manufacturing Apparatus for Semiconductor published by SCIENCE FORUM.
The basic washing process taken in this apparatus includes a step of dip-washing of the wafer with a solution of ammonia hydrogen peroxide heated to 80.degree., for example, a step of rinsing the solution with pure water, a step of etching by a dilute hydrofluoric acid, a step of rinsing the dilute hydrofluoric acid with pure water, and a step of dip-washing with a solution of hydrochloride hydrogenperoxide heated to 80.degree.. A step of rinsing the wafer with pure water is taken at the end.
Various solutions and pure water used in the steps are stored in individual washing tank. When the wafers are washed, about 25 sheets of semiconductor wafers, for example, are placed in a wafer basket of proper construction (as shown on page 241 of the above-identified prior art) and dipped in each tank according to the washing step.
However, the conventional apparatus has several problems. Since the various solutions and pure water are stored individually in the tanks arranged in the order of process to be taken, a plurality of numbers of tanks are required. For example, the prior art apparatus described above requires at least six tanks, resulting in a large size washing apparatus.
Moreover, one of the today's technical trend is to enlarge the diameter of the semiconductor wafers, and 8" diameter wafers are now on the market. As a result, large wafer baskets and tanks are inevitably required to treat 25-50 sheets of large wafers at once. For this reason also, a washing apparatus tends to be large in size.
Furthermore, it is difficult for a pure solution to evenly penetrates between wafers in the wafer dipping step, because spaces between the wafers in the wafer basket is very small (for example, about 4.75 mm). This results in uneven washing or etching. When dipping the wafers in the solution, the lower part of each wafer is dipped first and then the upper part. This time lag of the dipping causes another uneven washing. Thus, the uneven washing is more aggravated as the size of the wafers increases.
In addition, although new solutions and new pure water are constantly supplied into the tanks, the solutions and the pure water stored in the tank are not renewed completely at each washing step, and contaminated liquids tend to remain in each tank. As a result, the washing is not accomplished perfectly.